The use of plastic irrigation pipe or tubing to carry water to crops planted in fields is well known. Water is pumped from a pumping station into thin-walled pipe or flexible tubing. Earlier irrigation systems used rows of aluminum pipe having ports with gates. The gates were opened to release the water, which flowed down the rows, to thereby discharge water along its length into the soil. Placing several miles of these pipes was very labor intensive each Spring of the year because the aluminum sections were usually 30 to 40 feet long. Gradually, this prior system was replaced with thin-walled pipe or plastic tubing that is flexible enough to be rolled out from a large roll carried by a tractor. The outer end of the unrolled tubing is tied or closed off, and the other end is coupled to the pumping station for pumping water into the plastic tubing.
The known plastic tubing is very strong and holds a significant amount of water pressure. Once the thin, flexible tubing is filled with water, a known tool carrying at least one punch device on the end of an elongated handle is struck against the outer outside surface of the filled plastic tubing to penetrate the tubing and to thus form a hole therein. This is done by an individual carrying the tool having an elongated handle and swinging the cutting edge of the cutting tool mounted at the outer end of the elongated handle against the thin-walled pipe that is expanded outwardly under the pressure of the water contained therein. The pressure of the water is greater at distances that are closer to the pump where the holes formed in the tubing must be smaller. And as the holes are formed further away from the pump, they must be larger to get the desired substantially uniform discharge of water because less pressure exists in the tubing further from the pump. The current tool used to form such holes is heavy because it is made of metal with cutting elements welded to the four outer sidewalls of a cubically formed main body. The cutting elements are therefore integrally formed to the outside surface of the metal walls forming the cubical base. In addition to being too heavy, the cutting elements become dented during use and transporting from storage to the fields in which the irrigation tubing is being punctured.
Various types of cutting tools are known for cutting holes through sheet metal, metal containers, and the like. U.S. Pat. Nos. 893,043; 1,483,661; and 2,019,009 disclose various types of mechanical devices used to form openings through a package or container sidewall. The following patents show various types of circular cutting devices used to cut, saw, or punch circular openings in sheet material.
______________________________________ 580,916 2,086,435 3,203,295 4,010,543 1,789,729 2,145,725 3,726,545 4,277,891 ______________________________________
None of these prior art devices are capable of forming the openings desired in the irrigation tubing in the manner described above.